Stationary fire fighting systems have been developed for use in structures, chemical facilities and petrochemical plants for manufacturing or storage, such as existing buildings or new buildings, enclosed chemical plants, or enclosed or outdoor storage or manufacturing facilities. Stationary fire fighting systems with foam proportioning capabilities generally include a water flow meter, a controller, and a foam pump. The controller operates the foam pump based on the signal from the water flow meter to supply liquid foam concentrate or foamant to a water stream. The mixed foamant and water is then delivered through pipes in the building and sprayed with sprinklers to extinguish the fire. Currently, stationary foam proportioning systems use venturi-based technologies, such as in-line eductors, around-the-pump eductors, balanced-pressure systems, and other fixed-delivery mechanisms. However, these technologies can cause an undesirable pressure drop in water pressure. Reduced water pressure causes operating problems because the length of some pipes in buildings can be 400 to 500 feet or longer. To maintain full flow and maximize the effectiveness of the mixture being sprayed with the sprinklers, water pressure drop should be minimized.
In addition, balanced-pressure systems can be difficult to maintain. Bladder-type systems must be cleaned, the foamant must be disposed of, and the pressure vessels must be tested and reworked. During this maintenance time, the fire fighting system cannot be used and the building is left without protection. This maintenance work is also expensive, time consuming, and can cause environmental problems due to discarded foamant. During operation, balanced-pressure type foamant systems that use positive displacement pumps often “by-pass” foamant or recirculate foamant back to the foamant tank, which causes undesirable foaming and possible degradation of the new foamant in the tank.